Hitherto, for the purpose of removing ash from ash-rich coal, it has been known to use a process comprising stirring powdered coal together with a heavy hydrocarbon oil in the presence of water to form an oil containing aggregate of coal. However, this process has the deficiency that the cost of treatment is higher than in the case of using other processes, because about 20% by weight (based on the weight of the coal) of hydrocarbon oil is generally required. In order to overcome this deficiency, it has been proposed to use a process which comprises producing a coal-oil aggregate from a coal powder from which a fine powder part has been removed, and a process which comprises additionally adding a coal powder to the formed coal-oil aggregate. However, according to these processes, it is not possible to obtain a coal-oil aggregate having a desirably low oil content and having a satisfactory strength.
Another known process comprises stirring coal powder together with a light hydrocarbon oil in the presence of water to granulate the coal and separating the resulting coal granules and ash by means of a screen has been known. In this case, the process has the advantage that the light hydrocarbon oil can be reused by evaporating and then condensing it, but there is a deficiency in that the resulting coal granules are easily repowdered due to low strength.